Field of the Invention
This invention relates to a cleaning device. More specifically, this invention relates to a cleaning device which removes adhered substances on the surface of an image supporting body.
Description of the Related Art
As electrophotography image forming apparatuses, there are an MFP (Multi Function Peripheral) which has a scanner function, a facsimile function, a copying function a function of a printer, a data transmitting function and a server function, a facsimile device, a copying machine, a printer, and so on.
An image forming apparatus typically includes an image supporting body, an electrostatic charging unit, an expose unit, a developing unit, a transfer conveying unit, a cleaning device, a fixing portion, and so on. The image supporting body is cylindrical and rotatable. The electrostatic charging unit electrostatically charges the surface of the image supporting body uniformly. The expose unit exposes the image supporting body to generate an electrostatic latent image. The developing unit consists of a developer tank which stores toner, and a developing sleeve. The developing unit develops a toner image on the electrostatic latent image, by difference between electrical potential of the developing sleeve and electrical potential of the electrostatic latent image. The transfer conveying unit is placed facing the photo conductor, and electrical voltage of which the polarity is opposite to the toner image is applied to the transfer conveying unit. The transfer conveying unit conveys a transferring body such as a paper sheet, with transferring the toner image on the surface of the image supporting body to the transferring body. The cleaning device consists of a supporting part made of metal or the like, and an elastic body which is attached to the supporting part. The cleaning device scrapes off transfer remaining toner which was not transferred onto the transferring body and remains on the surface of the image supporting body. The fixing portion fixes the toner image on the transferring body, by applying heat and pressure to the toner image transferred onto the transferring body.
Recently, to reduce a downtime of an image forming apparatus, life prolongation of an image supporting body and a cleaning device is requested. When life prolongation of the image supporting body and the cleaning device is achieved, the number of times of replacement of the image supporting body and the cleaning device is reduced, and the downtime of the image forming apparatus can be reduced. As for the image supporting body and the cleaning device, the abrasion amount is an obstacle for life prolongation. When the abrasion amount exceeds a constant amount, they cannot exhibit the required functions. In such the case, the consumed component should be replaced with new one.
To reduce abrasion of the image supporting body and the cleaning device, it is effective to reduce stress which occurs at a contact portion between the elastic body and the image supporting body by reducing the contacting force of the elastic body of the cleaning device against the image supporting body. On the other hand, when the contacting force is too weak, the inhibiting power by which the cleaning device inhibits toner decreases. In such the case, cleaning failure is likely to occur. To decrease the abrasion of the image supporting body and the cleaning device and prevent the cleaning failure, the contacting force should be reduced, with decreasing variation of the contacting forces among cleaning devices.
At present, cleaning devices which are mainly used adopt a structure in which a rigid body is used as a supporting part, and a strip shaped polyurethane rubber component is used as an elastic body. According to the cleaning device having this structure, when the cleaning device makes contact with the image supporting body, the elastic body is elastically deformed. The repulsion of the elastic body is applied to the image supporting body as the contacting force.
According to the above-mentioned structure of the cleaning device, there is a lot of variation in reaction forces of the elastic bodies, caused by the variation of the deformation amounts of the elastic bodies and the Young's moduli. Hence, there is a problem in which there is a lot of variation in the contacting forces which make the elastic bodies contact with the image supporting bodies. Further, since polyurethane rubber has viscosity, when polyurethane rubber is pressed over the long term, permanent strain occurs in the elastic body. It degrades the cleaning power.
A cleaning device is proposed, in which a plate spring or the like is used as a supporting part, to give the supporting part flexibility and decrease the spring constant value of the supporting part. According to the cleaning device, when the elastic body makes contact with the image supporting body, both the elastic body and the supporting part become deformed. The variation in Young's moduli of metals is small, being different from characteristics of rubber. When the spring constant value of the rubber is small, peeling (buckling of the tip blade) occurs by the contacting force. Hence, it is difficult to decrease the spring constant value of the rubber. However, even though the spring constant value of the metal decreased, peeling does not occur in the metal. Therefore, it is easy to decrease the spring constant value of the metal. Hence, the variation of the contacting forces which make the elastic body contact with the image supporting body can be small, by applying flexibility to the supporting part, even though there is variation in deformation amounts of the supporting parts when the elastic body makes contact with the image supporting body. Further, since metal does not have viscosity, permanent strain does not occur in the metal.
An image forming apparatus uses toner to which lubricant is added. When toner is supplied to the image supporting body, and the toner passes through a nip portion between the image supporting body and the elastic body of the cleaning device, the lubricant becomes a coated layer. Hence, lubricating ability of the image supporting body improves. Herewith, frictional force acting between the toner and the image supporting body is reduced, and the cleaning performance of the cleaning device improves.
The supplied amount of lubricant to the image supporting body changes based on the toner amount being supplied to the image supporting body, i.e. the coverage of the document to be printed. Therefore, when the coverage of the document to be printed fluctuates, the friction coefficient of the image supporting body fluctuates, and the frictional force between the image supporting body and the elastic body fluctuates too. In consequence, the frictional force between the image supporting body and the elastic body changes based on the coverage of the document to be printed.
Especially, according to a cleaning device which includes a supporting part of which the spring constant value is small, when the frictional force between the image supporting body and the elastic body increases, it becomes easier for the supporting part to be deformed. In consequence, the contacting force which makes the elastic body contact with the image supporting body increases, so that it has a problem in that the lifeline of the image supporting body and the cleaning device shortens.
Further, when the supporting part is deformed, the oscillation of the supporting part increases. Then, there is a risk that a sound (abnormal noise) is produced, and the supporting part makes contact with the image supporting body to damage the image supporting body.
Documents 1 and 2 below discloses conventional cleaning devices, for example. The Document 1 discloses a cleaning device which includes a blade which makes contact with a surface of a photo conductor with pressure, supporting part to which the blade is fixed at the leading end, and a plate spring which makes the blade contact with the surface of the photo conductor with pressure via the leading end of the supporting part. The spring constant value of the plate spring is larger than the spring constant value of the supporting part.
The Document 3 below discloses a cleaning device which includes an elastic blade being pressed in an axial direction of a photo conductor, and a blade holder which holds the blade in the device main body. According to the cleaning device, the blade holder consists of a holder head which holds the blade, and a holder main body part which holds the holder head. The holder main body part is supported by the device main body via a shaft. The both ends of the elongated direction of the holder head is swingably about the axis of rotation of the head with respect to the holder main body, in directions opposite to each other.
[Document 1] Japan Patent Publication No. (HEI) 2-150885
[Document 2] Japan Patent Publication No. 2010-8776
According to the technique of Document 1, even though the frictional force between the photo conductor and the blade increases, the supporting part is pressed against the photo conductor by the plate spring. Hence, the blade is prevented from peeling. However, with increment of the frictional force between the photo conductor and the blade, the length of the leading end of the blade which is drawn into the rotation of the photo conductor increases, so that the contacting force which makes the blade contact with the photo conductor increases. In consequence, abrasion of the photo conductor and the blade increases, so that the lifetime of the photo conductor and the cleaning device shortens.
According to the cleaning device of Document 2, when the frictional force between the photo conductor and the blade increases, there is not a component which suppresses the force which occurs around its axis in the swing direction. Therefore, the contacting force which makes the blade contact with the photo conductor increases, and abrasion of the photo conductor and the blade increases, so that the lifetime of the photo conductor and the cleaning device shortens.
As described above, techniques described in Documents 1 and 2 have problems in that when frictional force between the image supporting body and the cleaning unit fluctuates, the contacting force which makes the elastic body contact with the image supporting body fluctuates too. Therefore, techniques described in Documents 1 and 2 have problems in which the abrasion amounts of the image supporting body and the cleaning unit fluctuate.
Namely, the problem in which the lifetime of the cleaning device shortens still remains in techniques described in Documents 1 and 2.